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EPR ‐based oximetric imaging: a combination of single point‐based spatial encoding and T 1 weighting
Author(s) -
Matsumoto Kenichiro,
Kishimoto Shun,
Devasahayam Nallathamby,
Chandramouli Gadisetti V. R.,
Ogawa Yukihiro,
Matsumoto Shingo,
Krishna Murali C.,
Subramanian Sankaran
Publication year - 2018
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.27182
Subject(s) - electron paramagnetic resonance , nuclear magnetic resonance , chemistry , relaxation (psychology) , in vivo , imaging phantom , analytical chemistry (journal) , spin–lattice relaxation , flip angle , magnetic resonance imaging , nuclear medicine , physics , optics , medicine , microbiology and biotechnology , chromatography , nuclear quadrupole resonance , biology , radiology
Purpose Spin‐lattice relaxation rate (R 1 )‐based time‐domain EPR oximetry is reported for in vivo applications using a paramagnetic probe, a trityl‐based Oxo71. Methods The R 1 dependence of the trityl probe Oxo71 on partial oxygen pressure (pO 2 ) was assessed using single‐point imaging mode of spatial encoding combined with rapid repetition, similar to T 1 ‐weighted MRI, for which R 1 was determined from 22 repetition times ranging from 2.1 to 40.0 μs at 300 MHz. The pO 2 maps of a phantom with 3 tubes containing 2 mM Oxo71 solutions equilibrated at 0%, 2%, and 5% oxygen were determined by R 1 and apparent spin–spin relaxation rate ( R 2 * ) simultaneously. Results The pO 2 maps derived from R 1 andR 2 *agreed with the known pO 2 levels in the tubes of Oxo71. However, the histograms of pO 2 revealed that R 1 offers better pO 2 resolution thanR 2 *in low pO 2 regions. The SDs of pixels at 2% pO 2 (15.2 mmHg) were about 5 times lower in R 1 ‐based estimation thanR 2 * ‐based estimation (mean ± SD: 13.9 ± 1.77 mmHg and 18.3 ± 8.70 mmHg, respectively). The in vivo pO 2 map obtained from R 1 ‐based assessment displayed a homogeneous profile in low pO 2 regions in tumor xenografts, consistent with previous reports onR 2 * ‐based oximetric imaging. The scan time to obtain the R 1 map can be significantly reduced using 3 repetition times ranging from 4.0 to 12.0 μs. Conclusion Using the single‐point imaging modality, R 1 ‐based oximetry imaging with useful spatial and oxygen resolutions for small animals was demonstrated.